I sometimes answered such a call with
Heddlu Dyfed-Powys Police, how can I help you?
My standard response when in work at Ops.
If they didn't hang up but asked for clarification I carried on with comments about my home number being diverted to police due to an ongoing investigation and could they please answer my questions. If they were still online I asked for their details, location, purpose of call etc. Most calls ended early but a couple didn't realise I was time wasting them.
Good fun if I had the time.
